1. Homeostasis Same State
maintaining a constant, internal environment within narrow limits, despite changes that take place internally and externally.

2. The conditions within cells depend on the conditions within the internal environment (tissue fluid).
Glucose , Carbon dioxide, Water, Salts, etc need to be kept constant within narrow limits.

3. General sequence of events in a negative feedback mechanism
Step 1: An imbalance is detected.
Step 2: A control centre is stimulated.
Step 3: Control centre responds.
Step 4: Message sent to target organ/s.
Step 5: The target organ responds.
Step 6: It opposes/reverses the imbalance.
Step 7: Balance is restored.
Can you use these steps to show regulation of glucose and thyroxin?

4. The regulation of carbon dioxide levels in the internal environment
When the CO2 level in the blood increases above normal levels:
Step 1 CO2 levels in the blood increase above normal levels
Step 2 Receptor cells in the carotid artery in the neck are stimulated
Step 3 To send impulses to the medulla oblongata in the brain
Step 4 Medulla oblongata stimulates breathing muscles (intercostal muscles and diaphragm) and heart
Step 5 Breathing muscles contract more actively – increases the rate and depth of breathing. The heart beats faster.
Step 6 More CO2 is taken to and exhaled from the lungs
Step 7 The CO2 level in the blood returns to normal

5. The regulation of water balance in the internal environment (osmoregulation)

6. The regulation of salt balance in the internal environment

7. Temperature regulation
Keeping body temperature as close to 37 ̊C as possible to enable the body to function normally. Control centre= hypothalamus Target organ= skin (sweat glands and blood vessels)

8. Skin

9. Hot day Cold day Control centre stimulated Hypothalamus Target organ
Skin
skin
Blood vessels to surface of skin
Dilate (vasodilation)
Constrict (vasoconstriction)
Blood flow to surface of skin
More
Less
Heat loss
Blood to sweat glands
Amount of sweat released and evaporated
Cooling of skin